function boompos(width,height,boomNum){
    var arr=[];
    var judge=0;
    for(var i=0;i<boomNum;i++){
        var w=Math.floor(Math.random()*width);
        var h=Math.floor(Math.random()*height);
        if(i==0) arr[i]=[h,w];
        else {
            for(var j=0;j<i;j++)
                if(h!=arr[j][0] || w!=arr[j][1]) judge+=1;
            if(judge==i){arr[i]=[h,w];judge=0;}
            else {i--;judge=0;}
        }
    }
    return arr;
}